This invention relates generally to methods for making polymer compositions, and, more particularly, to methods for making polymer compositions providing for improved flexibility in preparation in comparison to methods previously known.
Polymers are ubiquitous in modern products, used in a wide variety of consumer and specialty goods, by many different industries, such as electronics, aerospace, automotive, medical and sports industries. A variety of polymer are available for use in these industries, including commodity plastics, engineering plastics, thermosets, elastomers, and rubbers. However, often no single polymer exists that is suitable for a given application, and it often is difficult and expensive to develop a suitable new polymer. As a result, polymers are combined to prepare a polymer alloy or blend having desirable properties suited to the particular industry or application of interest. The polymers blended for a given application are selected to provide for optimum properties in the finished product with respect to performance, cost, and ease of manufacture.
Typically, polymer blends are prepared by taking the base polymers in their finished form and mixing them using a variety of known dry-blending or melt-mixing techniques. The resulting compositions are then processed as necessary for use in the intended product. Common blending methods include taking the polymer components, typically in the form of solid pellets or powders, and dry-blending them to make a heterogeneous composition. This heterogenous composition can then be melt-processed using a molding machine to make the required finished good. Alternatively, the polymer composition can be melt-mixed using calendring mills, or any type of internal mixer, such as an extruder or Banbury mixer. In mixing these blends, care is taken to select a proper type and design of mixing system, as well as to control related processing parameters, such as temperature, torque, screw speeds, and feed rate to produce blends having desirable properties. These dry and melt-mixing processes can be used in a variety of configurations, based on convenience and on the requirements of the particular polymer blend.
A variety of polymer blends have been disclosed that exhibit different properties. Examples of these blends and the mixing techniques used for producing them are illustrated in numerous U.S. Patents, including: U.S. Pat. No. 4,670,522 to Chen (melt-mixing of polyamides and poly(ether-ester) elastomers); U.S. Pat. No. 5,300,587 to Maca et al. (blending a perfluoropolyether and a thermoplastic polymer); U.S. Pat. No. 5,451,522 to Boardman et al. (melt-mixing of fluorochemical piperazine compounds and a thermoplastic polymer); U.S. Pat. No. 5,610,236 to Bonner (premixing followed by extruding of polyvinylchloride and polyketone); U.S. Pat. No. 6,140,498 to Yamashita et al. (melt-mixing composition of block copolymer and rubber); U.S. Pat. No. 6,217,982 to Dawson (melt-mixing of ethylene/alkyl (meth)acrylate with a blend of polypropylene, ionomer, ethylene/glycidyl acrylate or methacrylate copolymer, and uncrosslinked ethylene propylene rubber); U.S. Pat. No. 6,300,419 to Sehanobish (dry-blending followed by melt-mixing of propylene polymer compositions); U.S. Pat. No. 6,300,398 to Jialanella et al. (dry-blending followed by melt-mixing of homogeneous ethylene polymer, a wax, and a nucleating agent); U.S. Pat. No. 6,359,068 to Moren et al. (dry-blending followed by melt-mixing of polypropylene and thermoplastic copolymer); U.S. Pat. No. 6,362,258 to Avakian et al. (mix-melting of polyolefin, silica, antioxidant, and a co-additive); U.S. Pat. No. 6,380,303 to Ogoe (dry-blending or melt-mixing of polycarbonates and rubber-modified copolymers); U.S. Pat. No. 6,391,807 to Jariwala et al. (melt-mixing of a fluorochemical oligomeric compound and a thermoplastic or thermoset polymer).
Additional examples of polymer blends include those in which compatabilizer is added to allow blending of incompatible polymers, such as those described in U.S. Pat. No. 5,428,093 to Lee al. (polyethylene blend compositions prepared using compatibilizer with low and high density polyethylene) and U.S. Pat. No. 6,414,081 to Ouhadi (compatibilized blends of non-polar thermoplastic elastomers and polar thermoplastic polymers). Also, polymer blends have been prepared to form either a fully interpenetrating network (two independent networks of the polymer components penetrating each other, but not covalently bonded to each other), or a semi-interpenetrating network (at least one polymer component forms a linear or branched polymer interspersed in the network structure of another of the polymer components). Examples of such blends are described in U.S. Pat. Nos. 6,271,305 to Rajalingam et al. (elastomeric polyurethane interpenetrating network compositions prepared by in situ reaction of polyols with different isocyanates and polyisocyanates in bituminous material) and U.S. Pat. No. 6,355,735 to Wagner et al. (semi-interpenetrating polymer networkformed from epoxy monomer, one olefin monomer forming a co-monomer mixture with the epoxy monomer, and catalytic palladium compound). Blends also are prepared to include thermoplastic vulcanizates (TPVs) such as those described in U.S. Pat. Nos. 6,399,710 to Finerman et al. (thermolastic vulcanizates modified with a thermoplastic random copolymer of ethylene) and U.S. Pat. No. 6,329,463 to Abraham et al. (high-temperature, oil-resistant thermoplastic vulcanizates made from polar plastics and acrylate or ethylene-acrylate elastomers).
Polymer blends are particularly common in sporting goods, including athletic shoes, skis and ski equipment, snowboards, skates and skating equipment, bicycle components, football equipment, hockey equipment, soccer equipment, protective body gear, protective eyewear, golf clubs, and golf balls. Golf balls, in particular, extensively utilize polymer blends. Golf balls generally are constructed to include a core, at least one cover layer surrounding the core, and optional intermediate layers between the core and cover. A variety of polymer resins and blends of these resins are used to prepare compositions for making these layers. These resins are selected to optimize various ball properties, including speed, spin rate, and durability as demonstrated by shear-cut resistance.
In particular, ball covers have been prepared from balata, transpolyisoprene (“synthetic balata”), thermoplastic polyurethane, thermoset polyurethane, and ionomer, or blends of these. Golf balls incorporating balata covers provide for a soft “feel” when hit and high spin rate, which improves ball controllability, but they also exhibit poor shear-cut resistance. Examples of golf ball covers incorporating balata and additional materials are disclosed in U.S. Pat. No. 4,984,803 to Llort et al. (“the Llort patent”) and U.S. Pat. No. 5,255,922 to Proudfit (“the Proudfit patent”). The limitations of use of balata in covers with respect to poor shear-cut resistance are described in the Llort and Proudfit patents, as well as in U.S. Pat. No. 6,042,489 to Renard et al. and U.S. Pat. No. 6,368,236 to Sullivan et al.
To address the limitations of balata, other materials have been used in ball covers. For example, ball covers have been made incorporating high acid-content copolymeric ionomers, such as those disclosed in U.S. Pat. No. 5,298,571 to Statz et al. These covers provide for balls having superior durability and speed when hit, but they also provide poor “feel” and low spin rate. Covers also have been made from blends of copolymeric and terpolymeric ionomers, such as those disclosed in U.S. Pat. Nos. 5,120,791 and 5,328,959, both to Sullivan. These covers demonstrate improved feel and spin rate compared to those made only from copolymeric ionomers, and they exhibit reduced, but acceptable, shear-cut resistance and ball speed. However, use of these ionomers does not provide for complete flexibility. Ionomers exhibit ionic clustering, in which the metal cation-reacted functional groups cluster together due to the ionic attraction of the functional groups and the metal cations. This clustering is important in determining the physical properties and processability of the ionomers. However, ionomers as prepared have fixed levels of acid content and degree of reaction of the metal cation. As a result, the amount of ionic clustering in the particular ionomer, and the effect on properties of the ionomer, cannot readily be controlled.
In addition to use of balata and ionomers, covers also have incorporated thermoset polyurethane, such as is those disclosed in U.S. Pat. No. 6,132,324 to Hebert et al (“the Hebert patent”). Thermoset polyurethane covers provide good durability, feel, and spin rate, but these covers require complicated processing steps to mold the cover layer and to bring a full cure of the layer, as are described in the Hebert patent and in U.S. Pat. No. 6,328,921 to Marshall et al. Use of thermoplastic, rather than thermoset polyurethane, is described in, for example, U.S. Pat. No. 6,251,991 to Takasue et al. U.S. Pat. No. 6,369,125 to Nesbitt. Covers incorporating thermoplastic polyurethane provide for good feel, spin rate, and greater processability than thermoset polyurethane, but at the cost of poor shear-cut resistance. Also, the processing window (i.e., the range of suitable conditions for processing of the material) for thermoplastic polyurethane generally is narrower than for other thermoplastics used in making golf ball layers, leading to difficulties in manufacture.
Yet another approach for making golf ball cover compositions is to blend copolymeric or terpolymeric ionomers with elastomers. Such cover blends are disclosed in, for example, U.S. Pat. No. 6,371,869 to Kato et al. These blends provide good feel and high spin rate but, like blends of copolymeric and terpolymeric ionomers, they also provide for low shear-cut resistance and reduced ball speed. Additionally, blends of ionomers and elastomers can exhibit incompatibility between these components, leading to deterioration of ball performance and the need to use compatibilizers. Use of compatibilizers is described in patents discussed above, and also in, for example, U.S. Pat. No. 6,274,669 to Rajagopalan (golf ball covers incorporating ionomer blended with non-ionomer and compatibilizer).
Besides their use in ball covers, polymer blends also are used in golf ball cores, and in intermediate layers in multi-layer golf balls. The composition and resulting mechanical properties of the core are important in determining the ball's coefficient of restitution (C.O.R.), i.e., the ratio of the ball's post-impact to pre-impact speed, and its PGA compression, i.e., a measure of the deflection on the surface of the ball when a standard force is applied. A high C.O.R. improves ball speed and distance when hit, and generally, a high C.O.R. is achieved by having a high PGA compression. Golf ball cores generally are made from blends incorporating polybutadiene rubber. A number of patents discuss polymer blends for use in golf ball cores. For example, U.S. Pat. No. 6,239,222 to Nesbitt discloses cores comprising polybutadiene rubber and polypropylene powder resins. Also, U.S. Pat. No. 5,834,546 to Harris et al. discloses cores comprising polybutadiene rubbers and oxa acids, and U.S. Pat. No. 6,426,387 to Kim discloses cores comprising cobalt-catalyzed polybutadiene rubber having specified material properties. Many different compositions are used, either of multiple polybutadiene rubbers, or of rubbers with other compounds, to prepare ball cores having optimal properties.
The composition of intermediate layers is important in determining the ball's spin rate and controllability. These intermediate layers often are made using soft or hard ionomeric resins, elastomeric resins, or blends of these, similar to those used in cover layers. Like blends for golf ball covers, polymer blends for cores and intermediate layers are prepared generally by dry-blending and/or melt-mixing of the component polymers, along with any required additives or fillers. Examples of polymer blend compositions for intermediate layers are described in a number of patents, including U.S. Pat. No. 6,355,715 to Ladd, which describes an intermediate layer comprising polyether-type polyurethane and a second thermoplastic component, such as a block copolymer, dynamically vulcanized thermoplastic elastomer, or other listed components. Also, U.S. Pat. No. 5,253,871 to Viollaz describes intermediate layer compositions incorporating amide block copolyether and ionomer, and U.S. Pat. No. 6,124,389 to Cavallaro et al. describes intermediate layer compositions incorporating an ethylene methacrylic/acrylic acid copolymer and other specified thermoplastic components.
As discussed above, additional examples exist of use of blends of polymers in a variety of goods, prepared using a number of known techniques. Despite this wide variety, blending of these polymers has a number of disadvantages. Processing of the polymers can be difficult because of poor processability of selected polymers. Also, incompatibility of different polymers can lead to phase separation of the base polymers in the blend, with resulting deterioration of blend properties. Also, despite the wide array of available polymers, tailoring polymers to be used in blends to have optimum properties can be difficult. Any attempt to create a blend to meet a specific set of criteria is limited by the available materials and available methods for forming these materials. That is, despite the wide variety of polymer blends known, there continues to be a lack of ease and flexibility in preparing tailored polymer blends.
In view of the above, it is apparent that a need exists for improved methods for preparing polymer blends that provide for good processability, and tailoring of blend properties. The present invention fulfills this need and other needs, and provides further related advantages.